Hawaiian Climatology — LEOPOLD and STIDD 
At Honolulu and on the easterly coast of Oahu 
the surface wind is normally easterly at all hours 
with a maximum speed in the afternoon and a 
nocturnal minimum. Leopold (1948) relates 
this to surface stability at night. He showed 
that at Honolulu winds between 1,000 and 
2,000 feet have a maximum speed at night. This, 
apparently, is caused by horizontal convergence 
as the subsidence temperature inversion reaches 
its minimum height at night. 
CLIMATE IN RELATION TO CROPS AND 
VEGETATION 
Maps of the areas covered by different vegetal 
associations have been compiled by Ripperton 
and Hosaka ( 1942 ) . 
There is evidence of change in vegetation in 
certain areas, the most prominent being noted 
in the Waimea area of Hawaii where many 
square miles formerly in heavy forest now con- 
stitute a grassland containing large amounts of 
an introduced cactus. A local wind storm, known 
as "mumuku,” is said to have decreased markedly 
in frequency between 1830 and 1856. The 
change was attributed to the introduction of 
cattle and subsequent modification in vegetation 
(Anonymous, 1856 and 1926). 
In a series of papers, Das (1928, 1931 a,b) 
analyzed the relation of monthly sequences of 
temperature and rainfall to the production and 
quality of sugar. High-quality cane juice was 
apparently correlated with high temperatures 
during the first summer after planting and with 
cooler weather in the winter prior to harvest. 
Rainfall should be relatively low during the 
winter season and relatively high during the 
summer to produce the best quality of cane. 
Das found that a wet August in the summer 
prior to harvest was strongly correlated with 
high yield. 
BASIC DATA 
Few areas of comparable size have the large 
number of rain measurements made in Hawaii. 
Approximately 900 rain gages, most of which 
are kept by sugar and pineapple plantations and 
223 
by cattle ranches, are currently installed. About 
three-fourths of these gages are read daily. The 
data from 205 are published as daily values in 
Climatological Data; in addition there are 79 
stations for which monthly values only are pub- 
lished. A survey of basic rainfall data being 
collected currently has been made by Leopold, 
Burn, and Stidd ( 1948). 
Surface wind observations are few except on 
the island of Oahu and the only upper wind data 
are collected by the Weather Bureau from Ho- 
nolulu. 
For studies of phenomena of the lowest 4,000 
feet of the atmosphere, the location of the 
Honolulu Airport from which the Weather 
Bureau radiosondes are flown is poor. With 
respect to the trade winds the office is about 
8 miles leeward of the Koolau Range, whose 
peaks in this vicinity reach 3,000 feet. 
Forecasting at Honolulu is very dependent on 
reliable and continuous upper air observations 
at the existing ship stations and on Midway and 
Johnston Islands. Full use of pilot reports, par- 
ticularly in summer, will probably become more 
essential as improved techniques develop. 
DIRECTION OF FUTURE WORK 
The strong geographic patterns of rainfall 
totals should make the development of a scheme 
for quantitative short-range rainfall forecasts 
relatively simpler than in many other places. 
On the other hand, significant differences be- 
tween apparently similar areas on different 
islands loom large as potential difficulties. Four 
directions of work are necessary: (1) the defi- 
nition of criteria for expressing the strength of 
pressure troughs locally affecting the Hawaiian 
Islands; (2) the correlation of these criteria 
with rainfall quantities; ( 3 ) inter-correlation of 
rainfall between different stations or localities; 
and (4) an improved understanding of the 
structure of the high troposphere and lower 
stratosphere. 
To attain these ends certain groundwork is 
required. In connection with quantitative meas- 
ures of the importance of various upper air 
